Insulation - Vapour Barrier ?

Chief1975

I am laying some Wickes 100mm insulation down in the loft, replacing some old paper backed blanket stuff thats disintegrates when touched. According to my trusty Readers Digest DIY manual I need to put down a vapor barrier first ("reflective foil building paper or polythene sheets") between the joists. The instructions on the Wickes insulation doesn't mention anything about putting other material down first & I couldn't see anything that fits that description in Wickes anyway so is the info in the manual out of date?

economiser

No the info is not out of date. There have been several threads on this board recently about this and the problems that may result with condensation.

Chief1975

I have read through most of threads about condensation problems in the roof space but only found one mention of using a vapour barrier as preventative measure, with most people opting for extra ventilation instead?

Anyway seeing as the Readers Digest DIY manual is the bible, looks like I am off to Wickes to buy some of this:
http://www.wickes.co.uk/DPMs/Polythene-Vapour-Barrier/invt/152877

03022242

i design and specify new build properties, ive never had anyone mention a vapour barrier between the roof joists...condensation occurs in roof spaces because the insulation is pushed tight in to the eaves and thus blocks out any air in to the roof space..

oh ....and 100mm wont suffice, i would reccomend at least 200mm

Chief1975

I am using 100mm to replace the old paper backed stuff between the joists & then putting back the 170mm on top so its up to build regs.